Prevention and removal of sulfur deposits during the pipeline transportation of a sulfur-oil slurry

ABSTRACT

Method of preventing and removing sulfur deposition on the interior of pipe walls during the transportation of sulfur liquid-hydrocarbon slurries through pipelines by intermittently purging the lines with a neat liquid hydrocarbon under conditions capable of recovering and solubilizing any deposited sulfur on the pipe walls and thereafter repeating the cycle.

United States Patent Inventor Godfrey Q. Martin Moraga, Calif.

Appl. No. 827,937

Filed May 26, 1969 Patented Dec. 28, I971 Assignee Shell Oil Company New York, N.Y.

PREVENTION AND REMOVAL OF SULFUR DEPOSITS DURING THE PIPELINE TRANSPORTATION OF A SULFUR-OIL SLURRY 12 Claims, No Drawings Primary Examiner-Morris O. Wolk Assistant Examiner-Sidney Marantz AttorneysGeorge G. Pritzker and .I. H. McCarthy ABSTRACT: Method of preventing and removing sulfur deposition on the interior of pipe walls during the transportation of sulfur liquid-hydrocarbon slurries through pipelines by intermittently purging the lines with a neat liquid hydrocarbon under conditions capable of recovering and solubilizing any deposited sulfur on the pipe walls and thereafter repeating the cycle.

PREVENTION AND REMOVAL OF SULFUR DEPOSITS DURING THE PIPELINE TRANSPORTATION OF A SULFUR-OIL SLURRY BACKGROUND OF THE INVENTION sulfur does not undergo any undesirable change or the slurry: does not exhibit a tendency to wide variation in viscosity is essential to the process in addition to other problems which may be encountered during and after transportation of the slurry through a pipeline. Thus, agglomeration and separation of the sulfur from the carrier fluid, plating, depositing or coating of the sulfur on pipeline walls causing plugging of the pipeline, corrosion, particleattrition and viscosity changes dueto pressure and temperature variations requiring greater pumping power which increases operation costs, etc., are only a few of the problems normally encountered in transporting sulfur liquidhydrocarbon slurries through pipelines.

Although the above are serious problems for consideration in transporting sulfur through pipelines, nevertheless the I transportation of sulfur in slurry form through pipelines can be made to be an effective, attractive and economic means of sulfur transportation, particularly since sulfur is recovered or ob-' tained from isolated, remote and inaccessible areas, and must be transported to desired accessible areas. As noted above, a number of methods have been-proposed for pipeline transportation of sulfur slurries such as injecting molten sulfur into water or a liquid hydrocarbon thereby forming a sulfur slurry for pipeline transportation. These methods for making sulfur slurries suitable for transporting through pipelines generally do not overcome the agglomeration, attrition, deposition, sticking coating and/or plugging problems described above.

An object of the presentinvention is to transport sulfur asa A a pipeline and from which the sulfur can be readily recovered at the terminal end of the pipeline as essentially pure sulfur.

Another object is to transport sulfur as a liquid hydrocarbon slurry by pipeline over great distances under conditions of reduced pumping and handling costs and therein any deposited sulfur can. be readily removed from the interiorof the pipeline wall.'.

SUMMARY OF THE lNVENTION The present invention is directed to an improved novel and new technique of transporting sulfur liquid-hydrocarbon petroleum slurry through pipelines over great distances without the problem of having sulfur deposit on the interior of pipeline walls to a degree so as to cause increase in pumping costs, pressure drops or plugging of the lines, by intermittently terminating the flow of the sulfur liquid-hydrocarbon slurry and injecting into the lines a purging liquid hydrocarbon capable of dissolving any adhered sulfur from the pipeline'walls and thereafter repeating the cycle. The rate of dissolution and removal of the sulfur from the walls of the pipeline can be increased by maintaining the purging liquid hydrocarbon hot and at a flowing rate which is essentially the same as that of the slurry or which is preferably higher than that of the slurry and should be greater than at least 3 ft./sec. and preferably between about 5 and about 20 ft./sec. The purging or dissolving liquid hydrocarbon can range in viscosity from a light petroleum fraction such as liquified petroleum gas (LPG) to a crude oil and mixtures thereof. Preferred are liquid hydrocarbons containing naturally occurring sulfur solubilizers such as natural acidic components present in'crude oil, and described in copending application, Ser. No. 784,926, filed Dec. 18, 1968, asphaltene materials as described in copending application, Ser. No. 784,925, filed Dec. 18, 1968, and the like. The sulfur solubilizingor dissolving materials such as asphaltenic material if not naturally present in the liquid petroleum can be added in amounts of from about 0.1 percent to about 10 percent and suchliquid petroleum can be injected when necessary in various places along the pipeline where indications are that the slurry might cause sulfur agglomeration, deposition, sticking or plugging of the line. Any plugging detection means known in the art can be used for this purpose.

Incases where the purging liquid is injected into a sulfurdesalted'and dehydrated and the same applies to the liquid used as the carrier liquid for the sulfur slurry.

The liquid hydrocarbon carrier such as crude oil or fractions thereof can be dehydrated and desalted by any means known in the art such as described in Chemical Technology of Petroleum by Gruse and Stevens (2nd Ed.) p. 286, or as described in U.S. Pat. Nos. 2,257,997; 2,400,713; 2,830,957; 3,215,619; 3,346,508; 3,011,970; 3,294,676; 2,930,749; 2,998,383; 3,245,902; 2,140,574; 2,446,040; 2,971,905; 3,008,897 and 3,076,756. As stated any of these or other methods of desalti'ng and hydrating the liquid hydrocarbon carriers can be used provided that from the time the sulfur slurry is made and transported it is essentially free to salts such as halides of alkali-and alkaline earth metals e.g. NaCl and CaCl and has a nil water content preferably below 0.1 percent or-even below 0.05 percent based on the oil phase of the slurry.

lndehydrating oil, the oil such as crude oil can be allowed to settle in settlers to effect removal of water and thereafter heating to remove any entrained water. Thus, a crude oil containing above l percent water is allowed to stand in a tank for a period of time and the free water is removed and the crude oil is passed through several heat exchangers and dehydrators at around 200 F. to effect reduction of water to a level below about 0.04 percent.

Desalting can be accomplished by means of additives such as Tretolite DS-2l7 desalter which are injected into the oil, e.g. crude oil and hot water generally'containing soda ash is injected into the oil to effect removal of calcium sulfate. The emulsion is passed through heat exchangers and coalascers at an elevated temperature and finally to settlers where the salt solution -is withdrawn and the desalted oil dehydrated as described above.

The sulfur liquid-petroleum slurry can be made by any suitable means such as described in U.S. Pat. No. 2,798,772 or by the method described in copending patent application, Ser. No. 663,755, filed Aug. 28, 1967, Ser. No. 784,925, or 784,926, filed Dec. 18, 1968. lt is preferred that in the making of the sulfur-liquid petroleum fraction slurry that the sulfur be in spherical form and have particle size preferably of 20-450 microns since sulfur in this range size and form in the slurry is more stable and is more resistant to agglomeration, separation, attrition and friction.

The phase transfer method for making the sulfur slurry as described in the above-mentioned copending application comprises first forming a sulfur-aqueous liquid (water) slurry and thereafter phase-transferring the sulfur particles from the aqueous liquid into a liquid hydrocarbon. Thereafter, the crude oil can be added as desired.

The liquid petroleum carrier for the sulfur can be one ranging in viscosity from a light petroleum fraction such as liquified petroleum gas (LPG), gasoline, kerosene, fuel oil, lube oil, petroleum distillates, condensates, crude oil and mixtures thereof. Preferred are liquid petroleum containing at least .10 percent or higher of aromatics, preferably about 15-30 percent aromatic enriched kerosene or oil condensate fractions or crude oil containing 15-80 percent aromatics which include monoand polyaromatic hydrocarbons. I

The asphaltenic additive can be obtained from unrefined or refined crude oil and fractions thereof. By unrefined crude oil is meant any crude oil which has not been processed in a refinery. Thus, a crude oil may be used as it is removed from the ground, or it may be first processed in field units such as oil-water separators, degasers, etc. Although just how the asphaltenes function in the slurry mixture is not understood, it has been found that the asphaltenes prevent sulfur agglomeration, sticking and aid in the formation of spherical sulfur particles having dimensions of from to 800 microns and preferably between 20 and 450 microns.

The asphaltenes can be recovered from petroleum stocks by any suitable means such as described in the Journal of the Institute of Petroleum, Feb., 1968, pages 50-53 and Apr., 1968,

pages 107-114 or as described in U.S. Pat. Nos. 3,206,388; 3,228,870; 3,153,623; 2,729,589; 3,368,876; 3,364,138; 3,206,388 and 3,275,076. The latter two patents base materials can be used per se as the asphaltene additive and carrier for the slurry. In other words high asphaltenic crudes or fractions thereof containing at least 1 percent asphaltenes can be used both as the carrier and additive for the sulfur slurry. The asphaltenes, asphaltogenic acids and carboids and their method of recovery and separation from crudes and fractions thereof is also fully described in Chapter 9 of the Sachanens book on The Chemical Constituents of Petroleum? and includes petroleum resins, asphaltenic materials described in U.S. Pat. Nos. 3,275,076; 3,284,340 or 3,336,146 can be used and they can be separated from petroleum by methods described in U.S. Pat. Nos. 3,364,] 38 and 3,368,876.

Duringthe preparation of the slurry as the molten sulfur is dispersed into liquid petroleum containing preferably active asphaltenic components to aid in the making of spherical sulfur particles as well as prevent agglomeration, sticking and the like, the slurry can be cooled effectively by vapor cooling such as described in U.S. Pat. No. 2,632,691 or by use of volatile organic materials such as low-molecular-weight hydrocarbons or chlorinated hydrocarbons in which case the process should be carried out under pressures as described in U.S. Pat. No. 2,316,673 or by means described in copending application, Ser. No. 784,616 now U.S. Pat. No. 3,532,389 and 787,727, filed Dec. 18, 1968, and copending application to L. F. Bolger, Ser. No. 809,326 filed Mar. 21, 1969.

At the tenninal end of the line the sulfur can readily be separated from the slurry by any suitable means.

PREFERRED EMBODIMENT OF THE INVENTION I. A 40-60 percent sulfur aromatic (17 percent) enriched kerosene slurry was prepared by phase transfer by first injecting molten sulfur into an aqueous liquid such as water and thereafter contacting the slurry thus formed with aromatic enriched kerosene to effect phase transfer of the sulfur particles into the aromatic enriched kerosene. To the sulfur-kerosene slurry was added from about 1 percent to about 2 percent of asphaltenes and thereafter this slurry was injected into a pipeline for transportation to a terminal station. Sulfurkerosene slurries containing a small amount of crude oil thus formed do not form agglomerates nor did they plug the pipeline. Instead of using the phase transfer technique for making the slurry, molten sulfur can be injected into a liquid hydrocarbon, e.g. crude oil directly and admixed with a small amount( 1-2 percent) asphaltenes.

II. An advantage of the present process for transporting through pipelines sulfur liquid-petroleum slurries as defined is that the slurry can be also prepared by direct injection of molten sulfur into a suitable petroleum fraction such as kerosene, fuel oil, oil condensate or distillate, crude oil and mixtures thereof to which has been added a small amount of asphaltenes so as to aid in making spherical sulfur particles and prevent sulfur .agglomeration, deposition and plugging of pipelines. Either process as well as other processes can be used to make the sulfur liquid-petroleum fraction slurry depending on the availability of the carrier. Thus, where water is available the first process can be used and if not the second one canbe used.

The presence of a small amount of an asphaltenic material during the preparationof the slurry by method I or II has an additional advantage in that an asphaltenic material aids in the formation of spherical sulfur particles which are most desirable since spherical sulfur particles in slurries as defined provide optimum pipeline performance such as low pressure drops during itstransportation and ease of recovery and purification at the terminal end of the pipeline.

The following examples illustrate the essence of the present invention.

A. Molten sulfur at l50 C. was sprayed into aromatic (17 percent) enriched kerosene through a spray nozzle at about 200 p.s.i. pressure drop to give a homogeneous slurry with sulfur solids content of about 16 percent volume in which the sulfur particles were essentially larg'e-angular-crystalline particles which began to stick together and agglomerate into a sticky mass within about 10-15 minutes.

B. The method of A was repeated except that 1 percent of asphaltenes was added to the kerosene carrier. The particles formed were microspherical (20 450 microns) in shape and the tendency of the particles to stick or agglomerate were observed to have been greatly diminished.

After substantial quantities of sulfur slurry has been transported through a pipeline sulfur deposits will form at which time the injection of sulfur slurry is stopped and neat liquid hydrocarbon, such as neat crude oil, preferably hot 120-180 F.) is injected into the line to remove deposited sulfur therefrom and thereafter the cycle is repeated.

By this method of operation no shutdown problems are encountered, no mechanical means such as pigs are required to clean the lines and the lines are thus kept at maximum operating efficiency at all times and at a minimum of operating cost.

To illustrate the method of keeping pipeline transporting sulfur-oil slurries clean and operating at maximum efficiency, a sulfur-oil slurry prepared by the method described in copending application, Ser. No. 813,994, filed Apr. 7, 1969, now U.S. Pat. No. 3,547,497, in which the sulfur is added in increments so as to make a concentrated slurry containing 40 percent sulfur (40-350p.) in crude oil containing 0.5-5 percent asphaltenes and the concentrated sulfur slurry was injected into a pipeline and such slurries were transported through the line until pressure drop variations in the line was noted. Thereafter slurry injection was stopped and neat crude oil containing asphaltenes (0.1-1 percent) at a velocity in excess of 3 ft./sec. (3.5 ftJsec.) was injected and neat crude oil injection continued until the deposited sulfur on the pipe walls was removed and thereafter new su1fur-oil slurry injected and the cycle was repeated when necessary.

Instead of purging the entire line with neat oil, the sections of the line which is plugged with sulfur or where sulfur deposits on the walls of the line are heavy, can be isolated and purged with neat oil as described above to remove the sulfur and clean out that section of the line.

The efficiency of sulfur removal by this method can be increased by using hot oil rather than cold oil at a high velocity and the oil should preferably be desalted and dehydrated.

At the terminal end of the line the sulfur can be removed from the liquid hydrocarbon by suitable means such as described in U.S. Pat. No. 2,798,772 and the sulfur purified by methods as described in Ser. No. 684,507, filed Nov. 20, 1967, which comprises treating oil-contaminated sulfur with an aqueous solution containing a mixture of alkali hydrosulfide and corresponding hydroxide, e.g., ammonium hydrosulfide and ammonium hydroxide or by other suitable means such as sulfur can be recovered from the oil slurry by centrifugation or filtration of particulate sulfur, melting the particles and liquid-liquid extraction with a hydrocarbon solvent containing -50 percent aromatics. Thus, at the receiving terminal the sulfur slurry can be filtered and washed. The recovered sulfur is then melted and purified by liquid-liquid extraction with an aromatic hydrocarbon such as cumene. Also, if desired, the sulfur can be steam stripped to remove any dissolved solvent and then filtered to recover bright yellow sulfur.

The foregoing description of the invention is merely intended to be explanatory thereof. Various changes in the details of the described method may be made within the scope of the appended claims without departing from the spirit of the invention.

I claim as my invention:

1. An improved method of transporting a sulfur liquidhydrocarbon slurry through a pipeline while removing and preventing sulfur deposition on the interior of the pipeline wall, the steps comprising:

a. injecting into the pipeline a sulfur liquid-hydrocarbon slurry and flow-transporting said slurry through said pipeline;

b. terminating the injection and flow of the slurry (a) when sulfur deposition on the interior pipeline wall due to the normal affinity of sulfur to deposit in pipe walls is noted;

c. Injecting a neat liquid hydrocarbon into the pipeline at a flow velocity greater than that of the flow velocity of the slurry until any sulfur deposited as a result from step a has been removed from the interior surface of the pipeline by the neat liquid hydrocarbon;

d. reinjecting fresh a sulfur liquid-hydrocarbon slurry into the line as in step a; and

e. repeating steps a through d.

2. The method of claim 1 wherein the neat liquid hydrocarbon is injected only in the sections of the line which have been plugged with sulfur.

3. The method of claim 1 wherein the liquid hydrocarbon in steps a and c is a crude oil and in step a the flow rate of the slurry is at least 3 ft./sec. and in step c the neat crude oil flow rate is greater than 3 ft./sec.

4. The method of claim 3 wherein the neat crude oil is injected hot.

5. The method of claim 3 wherein the crude oil in steps a and c contains asphaltenes.

6. The method of claim 3 wherein the crude oil is dehydrated crude oil.

7. A method of preventing and removing sulfur deposition during pipeline transportation of a sulfur liquid-hydrocarbon a desalted.

slurry by intermittently injecting into said pipeline neat liquid hydrocarbon at a velocity greater than the velocity of the sulfur slurry flowing through the line.

8. The method of claim 7 wherein the velocity of the slurry is at least 3 ft./sec. and the velocity of the neat liquid hydrocarbon is greater than the velocity of the sulfur slurry flowing through the line.

9. The method of claim 7 wherein the hydrocarbon is crude oil.

10. The method of claim 9 wherein the crude oil contains asphaltenes.

11. The method of claim 9 wherein the crude oil is a desalted, dehydrated crude oil.

12. The method of claim 9 wherein the crude oil is hot crude oil. 

2. The method of claim 1 wherein the neat liquid hydrocarbon is injected only in the sections of the line which have been plugged with sulfur.
 3. The method of claim 1 wherein the liquid hydrocarbon in steps a and c is a crude oil and in step a the flow rate of the slurry is at least 3 foot/sec. and in step c the neat crude oil flow rate is greater than 3 foot/sec.
 4. The method of claim 3 wherein the neat crude oil is injected hot.
 5. The method of claim 3 wherein the crude oil in steps a and c contains asphaltenes.
 6. The method of claim 3 wherein the crude oil is a desalted, dehydrated crude oil.
 7. A method of preventing and removing sulfur deposition during pipeline transportation of a sulfur liquid-hydrocarbon slurry by intermittently injecting into said pipeline neat liquid hydrocarbon at a velocity greater than the velocity of the sulfur slurry flowing through the line.
 8. The method of claim 7 wherein the velocity of the slurry is at least 3 foot/sec. and the velocity of the neat liquid hydrocarbon is greater than the velocity of the sulfur slurry flowing through the line.
 9. The method of claim 7 wherein the hydrocarbon is crude oil.
 10. The method of claim 9 wherein the crude oil contains asphaltenes.
 11. The method of claim 9 wherein the crude oil is a desalted, dehydrated crude oil.
 12. The method of claim 9 wherein the crude oil is hot crude oil. 